1. Field of the Invention
The invention relates to a sound generation apparatus, particularly one employed with a computer system which includes a raster scanned display and a disk speed control apparatus.
2. Prior Art
There are countless well-known techniques for generating audio signals from digital signals. These include the more straightforward approaches where digital signals are used to provide an instantaneous amplitude of the audio signal, to the more complex vocoder techniques where transfer functions representative of voice are used. As will be seen, the present invention converts a digital signal to an analog (audio) signal, although this conversion is only one aspect of the present invention.
Most often, computer systems, particularly smaller systems (e.g., personal computers) employ raster scanned displays. The computer generates the video information and stores it in a random-access memory (RAM). Counters synchronize with the horizontal and vertical synchronization signals address the memory to provide display synchronized data signals from the memory. These signals are converted to a video signal, for instance, through a shift register. In some cases, the memory is "bit mapped" and the output from the memory is directly used to generate the video signal. In other cases, the output from the memory addresses a character generation which is scanned to provide video signals.
A considerable amount of data from RAM is required to generate a video display, particularly in a dynamic, graphics (non-text) mode. In the personal computer field, or small business computer field, where microprocessors are used along with dynamic RAMs, the generation of a video display consumes a relatively large amount of processor and memory time. It is thus difficult to provide an audio signal, particularly a complex audio signal in a display mode.
As will be seen, the present invention provides an apparatus for generating audio signals in conjunction with a microprocessor and RAM simultaneously with the generation of video signals. The audio signals are generated without disrupting the video display or computer operation, and importantly, with a minimum of hardware and processor time.
Typically, in floppy disk drives, some mechanism is employed to drive the floppy disk motor at a constant speed. When the floppy disk drive is manufactured, certain calibration steps are often used to assure that the floppy disk drive runs at a predetermined rate of rotation. This requires, in addition to the calibration steps, relatively costly speed control mechanisms. As will be seen, in the present invention, the computer is used to sense the rate of rotation of the disk drive and then provides a control signal to adjust the disk drive's rate of rotation. This eliminates the prior art calibration and also the prior art's speed control mechanism.
It has been suggested in the prior art that better utilization of floppy disks or other disks can be obtained if uniform flux density transitions are used. This requires that the rate of rotation of the disk be made a function of the radius of the particular track being accessed. The present invention provides such a feature.